The study of the physiological response of a human to various sounds has increased in recent years. The effects of music, for example, on humans of various ages has been studied using sophisticated electrophysiological monitoring apparatus, such as electroencephalographs, electrocardiographs, electromyographs and even MRI scanners. Attempts have been made, for example, to determine whether or not music has a positive effect on the functioning of the brain while performing tasks such as mathematical problems.
In the industrial arena noise, vibration and harshness (NVH) effects have been studied in the automotive field. The general approach to such studies has been to try to isolate, eliminate or reduce the NVH level in automobiles so that the user does not have to endure long periods of time during which he or she is exposed to NVH levels that cause fatigue, irritability and/or drowsiness.
Studies directed to the effects of sound on humans also have included subjective approaches. Thus, panels or juries are asked to subjectively rank sound quality as between categories, such as, rough, sharp, metallic, whiney and hollow. Using such subjective rankings by panels of listeners the goal has been to try to predict sound-quality preferences, that is, to try to quantify in some manner the subjective impressions of the panel.
In some cases it is possible to simply isolate the user from the sound output, but in many cases such isolation is not practical or even possible. Moreover, in some instances, the sound output of a product can actually be pleasing, or made to be more pleasing. Thus, it has been a common experience in connection with mufflers for internal combustion engines that some mufflers will attenuate sound in a manner which is effective as to the decibel level, but nevertheless is irritating, stressful or unpleasant. Other mufflers, by contrast, are known to be subjectively more pleasing to the driver. Exactly why one muffler is annoying, while the other is pleasing, is only known in a general subjective sense, namely, that one has a harmony of sound or a consonance which is more appealing to the driver and to persons past whom the vehicle is driven.
Sound output which has intellectually perceivable sound content, such as advertising, also has been studied by sensing electrophysiological responses of subjects. Thus, in U.S. Pat. No. 5,243,517, subjects listen to a plurality of proposed advertisements having different intellectually perceivable content and their physiological responses to the changed advertisements are sensed. The subjects' physiological responses to content changes were then used to select as between advertisements.
Accordingly, it is an object of the present invention to provide a process and apparatus for selecting or designing products, such as exhaust mufflers for internal combustion engines or other products having content-free sound outputs, which resulting products produce an objectively demonstratable lessened mobilization of the body's stress response mechanisms, or a more pleasing physiological response in humans.
A further object of the present invention is to provide a process and apparatus for producing or choosing a product having a multi-frequency, content-free sound output in which electrophysiological monitoring techniques are employed to objectively enhance product design or selection.
The process of the present invention has other objects and features which are set forth in, or will be apparent from, the following Best Mode of Carrying Out the Invention and the accompanying drawing.